Regenerative heat exchanger



Jan. 11, 1966 G. SCHOLL 3,228,457

REGENERAT IVE HEAT EXCHANGER Filed Aug. 17. 1960 INVENTOR GU/VTE-R SCHOLL ATTORNEYS United States Patent 3,228,457 REGENERATIV'E HEAT EXCHANGER Giinter Schiil], Mulhergerstrasse 21A, Esslingen (Neckar), Germany Filed Aug. 17, 1960, Ser. No. 50,272 Claims priority, application Germany, Sept. 9, 1959, Sch 26,662 5 Claims. (Cl. 165-7) The present invention relates to a regenerative heat exchanger which consists of a rotor which is mounted and rotatable within a stationary housing and providing with a a heat-retaining mass through which alternately the heatsupplying and the heat-absorbing media are adapted to how. Regenerative heat exchangers of this general type, also called Ljungstrom regenerative preheaters, are known in the prior art in many different designs. Although these known preheaters have, on the one hand, the advantage that relatively large heat-retaining masses may be provided therein in a relatively simple manner, they have, on the other hand, a series of very serious disadvantages which practically nullify the mentioned advantage and reduce the utility of the apparatus to a considerable extent.

One very important disadvantage of these known regenerative preheaters which limits their use in actual practice consists in the fact that they require very large heatretaining masses of a great heat capacity since the temperature differences of these masses while revolving from the heatdelivering side to the heat-absorbing side may be only very small and amount, for example, to only 20 C. In comparison to a heat exchanger with solid partitions it may therefore be said that the heat-retaining mass moves in the case of these known preheaters in a crosscurrent relative to the media which participate in the heat exchange.

It is an object of the present invention to provide a regenerative heat exchanger which possesses the advantage of the well-known Ljungstrom preheater, namely, the provision of relatively large heat-retaining masses, but which avoids the disadvantages of this known preheater, namely, the low temperature difiference which can only be utilized therein because of the movement of the heat-retaining masses in a direction vertical to the flow of the two media in accordance with the crosscurrent principle.

For attaining this object, the present invention provides that the heat-retaining mass which is disposed in an annular arrangement along the periphery of the rotor is divided into individual sectors by means of intermediate valve elements which are operated in response to their particular position during the rotation of the rotor, so that during the heat exchange the heat-supplying and heatabsorbing media will flow in two separate currents through the heat retaining mass in a direction opposite to the direction of rotation of the rotor. During this flow those heaPretaining masses which are heated to the highest temperatures will always come into contact with that part of the medium which is to he preheated which has already taken up most of the heat, while those heat-retaining masses which have already been cooled off to the greatest extent will come into contact with that part of the other medium which has already given off most of its heat. In this manner it has been possible to apply the counter-cur rent principle almost ideally to the heat-retaining masses both insofar as the heat delivery as Well as the heat absorption is concerned which, in turn, means that the high- "ice est possible heat transmission will be attained in accordance with the heat capacity of the heat-retaining mass and the speed of the rotation thereof. This heat transmission which is attained according to the invention is so great as compared with that of the conventional Ljungstriim prehcater that, at each revolution of the rotor carryin" the heat-retaining mass, each particle of the latter will utilize a much greater temperature gradient, namely, one about ten to twenty times as great as that of a Ljungstrom prcheater. If the speed of rotation of the preheater according to the invention is, for example, the same as that of a Ljungstrio'm preheater, the weight of the heat-retaining masses of the new type of preheater may be reduced to about one-tenth or one-twentieth of the weight of the heat-retaining masses of a Ljungstriim preheater. If, on the other hand, the same amount of heat-retaining masses is applied in a preheater according to the invention as in a Ljungstrom preheater, the transmission of the same amount of heat will only require the speed of the rotor of the new preheater to be one-tenth or less of the speed of the rotor of a Ljungstrom preheater.

A further advantage of the regenerative heat exchanger according to the invention over the conventional Ljungstriim preheater is that any particular amount of heat to be transmitted is directly coordinated with a very particular optimum speed of the heat-retaining mass. It is thus possible to lower the degree of efficiency of the heat transmission by varying the speed of rotation of the rotor carrying the heat-retaining mass. This may be very important, for example, if the temperature of the heat-retaining masses or of the heat-receiving medium should not exceed a certain maximum.

A still further and very important advantage of a heat exchanger according to the invention in which the heatretaining mass revolves according to the countercurrent principle consists in the fact that, since the heat transmission is also dependent upon the product of the heat capacity of the heat-retaining mass times the speed of rotation thereof, it is possible by a suitable selection of the peripheral speed of the rotor and thus also of the heat-retaining mass to adjust within wide limits the lowest and highest admissible temperatures of the heating sur faces, that is, the range between the point of condensa tion and the point of scaling of these surfaces' The inlets and outlets for the heat-supplying and heatreceiving media may be provided in such a position on the stationary housing which surrounds the rotor that at first the two media will flow into the heat-retaining mass in a substantially radial direction, then through the mass in the peripheral direction of the rotor, and finally out of the mass again in a substantially radial direction.

According to another feature of the invention, during the continuous rotary movement the individual valve elements will always be closed when they arrive at the inner edges of the gas inlets, and they will again be opened when they arrive at the inner edges of the adjacent outlets and then remain open in all other positions during their rotation. By this controlled operation of the valve elements it is possible to seal the path of the current of the heat-delivering medium from that of the heat-absorb ing medium so completely that the two media will never become mixed at any point of the heat exchanger,

A further feature of the invention consists in the fact that, if any desired number n of valve elements is distributed in the peripheral direction of the rotor, each of these elements will during one revolution of the rotor be closed twice for at least 1/11 of the length of time of one revolution, while the distance between the adjacent inlets and outlets amounts at least to the size of 1/ n of the outer periphery of the rotor.

In order to insure absolutely that the valve elements will always be properly operated at the right time, it is advisable to control the opening and closing movements of these elements in response to or in synchronism with the rotary movement of the rotor. This may be effected either by mechanical means, for example, by cams, rods, tappets, or the like. In some cases it may be desirable to apply other and equivalent means such as fluid pressure actuated means, for example, hydraulic means.

The valve elements may consist of shut off valves or slide valves, although it is also possible to provide pivoted flaps or shutters or groups thereof. The individual shutters of each group are then preferably arranged in the radial direction behind each other and are actuated by a common rod connecting the same. In order to insure that the individual shutters will close tightly, spring element-s may be provided between the shutters and the common connecting rod.

The heat-retaining mass may consist of any desired arrangement of a material which is suitable for this purpose. One arrangement which has proved to be especially effective consists of a series of coil springs which because of their large surface area and the small wire thickness produce a relatively high heat transmission and will thus transmit relatively large amounts of heat. The heatretaining masses may, however, also consist of sets of flat sheet-metal plates with intermediate spacing members or wartlike projections, or of sets of corrugated sheet-metal plates.

The two ends of the rotor are preferably provide-d with annular disks which are sealed relative to the stationary housing. The sealing means for sealing the inside of the rotor from the outer air preferably consist of slip rings which are preferably composed of individual segments, or of asbestos packing rings, asbestos cords, or the like which are acted upon by compression springs and form a tight seal along the outer wall of the stationary housing as well as along the inner surfaces of the revolving disks. By such sealing means it is possible to prevent practically any leakage losses.

The means for driving the rotor at a speed which, depending upon the particular size and construction of the regenerative heat exchanger, only has to amount to to 15 revolutions per hour, preferably consist of friction rollers which not only rotate the rotor at the annular disks thereof but also support the same. If the heat exchanger only has to .be of a smaller and therefore lighter size, it is, of course, also possible to support and drive the rotor by means of a central shaft.

If the heat-supplying and heat-absorbing media are passed in a countercurrent through the heat-retaining masses which are mounted peripherally on the rotor, losses in pressure will be incurred which, in turn, result in differences in pressure between the adjacent inlets and outlets. This, however, means that the media which flow into the rotor while still under a higher pressure will exert a pressure which is opposed to the direction of their flow upon the closed valve elements forming a partition between each inlet and the adjacent outlet. By this pressure, the media themselves will assist in rotating the rotor in a direction opposite to the direction of their flow. If the heat exchanger according to the invention is suitably designed and if the pressure conditions of the inflowing media are suitable, it will even be possible to utilize the above-mentioned fact to such an extent that 110 motor at all will be required to drive the rotor.

F or avoiding any undue heat losses and, on the other hand, any excessive thermal stresses on the material of the rotor and the annular disks thereon, as well as on the stationary housing, the heat-retaining mass should he insulated toward the outside by suitable insulating walls.

The above-mentioned as well as additional objects, features, and advantages of the present invention will :become further apparent from the following detailed description thereof which is to be read with reference to the accompanying drawings, in which:

FIGURE 1 shows a vertical section of a regenerative heat exchanger according to the invention; while FIGURE 2 shows a side view thereof, partly in a cross section taken along line A-B of FIGURE 1.

In these drawings, the regenerative heat exchanger according to the invention is illustrated as comprising a rotor 1 in the form of a hollow cylinder which carries on each end an annular disk 2 and is surrounded'by a stationary cylindrical housing 3. Rotor 1 including disks 2, as well as housing 3 are protected from the heat of the heat exchanging means by insulating layers 4 so that any changes in size or tensions in the material due to the temperature influences will be avoided.

The stationary housing 3 further carries the inlets and outlets 5, 7 and 6, 8 for the entry and discharge of the two media, for example, of the flue gases to be cooled and of the air to be preheated. By means of its disks 2, rotor 1 rests on friction rollers 9 which are driven from the outside by suitable means, not shown, so as to drive rotor 1 in the direction as shown by the arrow 11. Instead of driving rotor 1 by means of the rollers 9, it is, however, also possible to do so by providing a central drive shaft 12, as indicated diagrammatically by dot-anddash lines, which is then supported by suitable bearings.

The annular space which is enclosed by the components 1, 2 and 3 is divided by valvelike elements, for example, individual groups of hinged vane-type shutters 13, into individual sectors 14 in which heat-retaining masses are mounted which may consist, for example, of coil springs 15 which insure an excellent heat transmission, or of sets of flat sheet-metal plates 16 which are separated by spacing members, or of sets of corrugated plates 17 which are disposed at right angles to each other.

In order to prevent the media which flow into the heat exchanger under pressure from escaping, it is necessary to seal the annular slot between the stationary housing 3 and the disks 2 of rotor 1. This may be attained by different means, two of which are indicated in FIGURE 2. Thus, for example, a slip ring 18 which may be composed of several segments may be placed around the outer peripheral wall of housing 3, as shown adjacent to the right end thereof, and this slip ring may be acted upon by compression springs 19 in such a manner that its outer edge will slidably engage with the inner surface of disk 2 and thus form a tight seal. Since this slip ring 18 is mounted on the outside of housing 3, it is likewise protectedby the insulating layer 4 from the heat of the gases and may be easily lubricated with oil, grease, or the like. The sealing means may, however, also consist of an asbestos cord 21 which forms a continuous ring and is placed around the outer wall of housing 3. This asbestos ring 21 may be pressed by springs 22 against the respective disk 2, as indicated at the left side of FIGURE 2, and will thus seal the gap between rotor 1 and the stationary housing 3.

The means for supporting the stationary housing 3 with the inlets and outlets 5 to 8 thereon relative to rotor 1 which revolves together with the heat-retaining mass 15, 16, or 17 and the valvelike elements 13 may be of any suitable kind and need not be particularly described. It will suflice to say that housing 3 is preferably made of a light construction, for example, of thin sheet metal, and is, in turn, supported by rollers on the lateral disks 2. The Weight of the apparatus is then borne by the foundation through disks 2 and friction rollers 9.

The operation and effect of the heat exchanger according to the invention and the control of the valvelike elements are as follows:

Rotor 1. which carries the. heat-retaining mass 15, 16,

or 17 and revolves very slowly in a direction opposite to the direction of flow 23-24 of the two heat-supplying and heat-absorbing media, is shown in FIGURE 1 in a position in which the two sets of shutters 13', after passing the inlets 5 and 7, have just been closed so that the hollow space surrounded by the components 1, 2, and 3 will be divided into two entirely separate annular channels 25 and 26, each of which extends along an angular distance of about 150. If a current of hot flue gases passes into the annular channel 25 through socket 5, it will at first flow in a substantially radial direction into the set of heat-retaining masses which at that particular time is located adjacent to inlet 5, and it will then continue to flow in the direction of arrows 23 through the open sets of shutters 13 and the heat-absorbing masses 15, 16, or 17 between inlet 5 and outlet 6. Finally, the current will again flow in a substantially radial direction out of the particular set of heat-absorbing masses which is then adjacent to outlet 6 and out of that outlet. The air which is to be heated then flows in the same manner, but in the opposite direction, as indicated by arrows 24, through inlet 7 into the annular channel 26, where it absorbs the heat which is stored by the heat-absorbing masses, and then flows out through outlet 8.

At the particular time in the operation of the apparatus, as illustrated in FIGURE 1, when the sets of shutters 13' are closed, the two adjacent sets 13" are still likewise closed. The two media must therefore follow their ascribed path without becoming mixed with each other at any point. In the course of the rotation of rotor 1, the individual shutter sets 13 will then be closed when passing the inner edges 5' and 7 of inlets 5 and 7, and they will remain closed until they have reached the inner edges 6' and 8' of outlets 6 and 8. At this time, the respective shutters 13 will again open so that the media can pass freely through the annular channels 25 and 26, respectively. The two sets of shutters 13" as shown in FIGURE 1 will therefore open immediately after they have passed the position illustrated and will then permit the respective medium to pass into the outlet 6 or 8, respectively. The particular shutters 13 will then remain in the open position until they have again reached the inner edge 5' or 7' of the following inlet 5 or 7, respectively.

The operation of shutters 13 is preferably controlled by the rotary movement of rotor 1, for example, by mechanical means in the form of stationary cams 27, rods, tappets, or the like, each of which is operatively associated with a rod 28 which is connected to one set of shutters 13 so as to open or close the latter. Shutters 13 may, however, also be controlled by fluid pressure actuated means, as indicated diagrammatically in FIGURE 2 by a control rod 31 which is hydraulically controlled by a piston 29.

In order to close the individual shutters 13 of each set as securely as possible, each of them is preferably provided with a separate spring, not shown, which is connected to the common connecting rod 28. In this event, if a foreign body should enter with the heat-supplying current and should settle on one of the shutters of one set and thereby prevent the same from closing tightly, the resilient pressure of the other shutters of this set when closed by the common connecting rod 28 will prevent them from being also affected by the same foreign body and will insure that they at least will close tightly.

The regenerative heat exchanger according to the invention may be modified in numerous ways.

Having thus fully disclosed my invention, What I claim is:

1. A regenerative heat exchanger comprising a station ary housing, a rotor mounted to rotate within said housing, heat exchanging material carried by said rotor, said rnaterial providing a plurality of passages for fiow of gaseous fluid media therethrough peripherally of said rotor, valve means carried by said rotor comprising a plurality of sets of valve members arranged to divide said rotor into a plurality of sector shaped compartments each containing a separate mass of said material, each of said sets of valve members when closed being operative to separate contiguous compartments and when open providing for free flow of fluid through contiguous compartments from an inlet to an outlet of the apparatus, a first inlet and a first outlet for high temperature heat delivering fluid peripherally spaced in said housing and located on the same side of a plane coincident with the rotor axis, a second inlet and a second outlet for low temperature heat absorbing fluid peripherally spaced in said housing on the opposite side of said plane, said first and said second inlets and outlets being located respectively on opposite side of a second plane coincident with said rotor axis and normal to the first mentioned plane, whereby to provide paths of flow for the gaseous media in the same direct-ion peripherally with respect to the rotor axis through the apparatus in different streams on opposite sides of the first mentioned plane, means for positively opening and closing said sets of valve members in preselected positions relative to said inlets and said outlets to maintain said different streams separated from each other, means for turning said rotor in a direction opposite to that of the direction of flow of said streams through the rotor, said rotor comprising an axially extending central wall portion connecting two axially spaced outwardly extending disk portions and insulating material carried by said central and disk portions with said insulating material interposed between the gaseous media and said central and disc portions and forming the radially inner wall and the end walls of said paths of flow for said fluids and said housing comprising an insulated substantially cylindrical shell providing the radially outer wall of said paths of flow, whereby the portions of the walls of said paths of flow formed in said rotor are lined with insulating material operative to minimize distortion and misalignment of the structure of the rotor and the valve means carried thereby by reducing differential heat flow between said rotor structure and said gaseous media.

2. A heat exchanger as defined in claim 1 in which at least a portion of said shell is provided with an inner lining of insulating material providing the radial outer wall for said paths of flow, whereby insulating material is interposed between said gaseous media and the supporting structure for the walls of said paths of flow over substantially the entire area of said walls.

3. A regenerative heat exchanger as defined in claim 1 in which each of the disc portions of the rotor cooperates with and rests on a plurality of rollers rotatable around their axes which are fixed in relation to said stationary housing.

4. A regenerative heat exchanger as defined in claim 3 in which each of said rollers is provided with grooves in which the disc portions of the rotors are located for axial fixation of the rotor.

5. A regenerative heat exchanger as defined in claim 1 in which sealing means are nonrotatably mounted on the stationary housing and located outside the surface thereof facing the heat exchanging material and the valve means, said sealing means being axially slidable and provided with means for moving said sealing means into sealing proximity to the axially inner surfaces of said disc portions of the rotor.

References Cited by the Examiner UNITED STATES PATENTS 1,603,026 lO/ 1926 Cook -8 1,843,252 2/1932 Toensfeldt 1657 2,151,356 3/1939 Queen 277-424 2,344,884 3/ 1944 Altenkirch 165-3 (Other references on following page) 7 UNITED STATES PATENTS- Horn 165-9 Jonkers 165-1'0 Kennedy 1*37-601 sMunters 183-4.6

Odman 1'65166 Sandman et a1 1655' Kurth et a1 137-601 8 3,049,985 8/1962 Klingberg 137-601 3,108,632 10/1963 Jensen et a1. 1659 FOREIGN PATENTS 126,903 12/ 1949 Sweden.

ROBERT A. OLEARY, Primary Examiner.

HERBERT L. MARTIN, CHARLES SUKALO,

Examiners. 

1. A REGENERATIVE HEAT EXCHANGER COMPRISING A STATIONARY HOUSING, A ROTOR MOUNTED TO ROTATE WITHIN SAID HOUSING, HEAT EXCHANGING MATERIAL CARRIED BY SAID ROTOR, SAID MATERIAL PROVIDING A PLURALITY OF PASSAGES FOR FLOW OF GASEOUS FLUID MEDIA THERETHROUGH PERIPHERALLY OF SAID ROTOR, VALVE MEANS CARRIED BY SAID ROTOR COMPRISING A PLURALITY OF SETS OF VALVE MEMBERS ARRANGED TO DIVIDE SAID ROTOR INTO A PLURALITY OF SECTOR SHAPED COMPARTMENTS EACH CONTAINING A SEPARATE MASS OF SAID MATERIAL, EACH OF SAID SETS OF VALVE MEMBERS WHEN CLOSED BEING OPERATIVE TO SEPARATE CONTIGUOUS COMPARTMENTS AND WHEN OPEN PROVIDING FOR FREE FLOW OF FLUID THROUGH CONTIGUOUS COMPARTMENTS FROM AN INLET TO AN OUTLET OF THE APPARATUS, A FIRST INLET AND A FIRST OUTLET FOR HIGH TEMPERATURE HEAT DELIVERING FLUID PERIPHERALLY SPACED IN SAID HOUSING AND LOCATED ON THE SAME SIDE OF A PLANE COINCIDENT WITH THE ROTOR AXIS, A SECOND INLET AND A SECOND OUTLET FOR LOW TEMPERATURE HEAT ABSORBING FLUID PERIPHERALLY SPACED IN SAID HOUSING ON THE OPPOSITE SIDE OF SAID PLANE, SAID FIRST AND SAID SECOND INLETS AND OUTLETS BEING LOCATED RESPECTIVELY ON OPPOSITE SIDE OF A SECOND PLANE COINCIDENT WITH SAID ROTOR AXIS AND NORMAL TO THE FIRST MENTIONED PLANE, WHEREBY TO PROVIDE PATHS OF FLOW FOR THE GASEOUS MEDIA IN THE SAME DIRECTION PERIPHERALLY WITH RESPECT TO THE ROTOR AXIS THROUGH THE APPARATUS IN DIFFERENT STREAMS ON OPPOSITE SIDES OF THE FIRST MENTIONED PLANE, MEANS FOR POSITIVELY OPENING AND CLOSING SAID SETS OF VALVE MEMBERS IN PRESELECTED POSITIONS RELATIVE TO SAID INLETS AND SAID OUTLETS TO MAINTAIN SAID DIFFERENT STREAMS SEPARATED FROM EACH OTHER, MEANS FOR TURNING SAID ROTOR IN A DIRECTION OPPOSITE TO THAT OF THE DIRECTION OF FLOW OF SAID STREAMS THROUGH THE ROTOR, SAID ROTOR COMPRISING AN AXIALLY EXTENDING CENTRAL WALL PORTION CONNECTING TWO AXIALLY SPACED OUTWARDLY EXTENDING DISK PORTIONS AND INSULATING MATERIAL CARRIED BY SAID CENTRAL AND DISK PORTIONS WITH SAID INSULATING MATERIAL INTERPOSED BETWEEN THE GASEOUS MEDIA AND SAID CENTRAL AND DISC PORTIONS AND FORMING THE RADIALLY INNER WALL AND THE END WALLS OF SAID PATHS OF FLOW FOR SAID FLUIDS AND SAID HOUSING COMPRISING AN INSULATED SUBSTANTIALLY CYLINDRICAL SHELL PROVIDING THE RADIALLY OUTER WALL OF SAID PATHS OF FLOW, WHEREBY THE PORTIONS OF THE WALLS OF SAID PATHS OF FLOW FORMED IN SAID ROTOR ARE LINED WITH INSULATING MATERIAL OPERATIVE TO MINIMIZE DISTORTION AND MISALIGNMENT OF THE STRUCTURE OF THE ROTOR AND THE VALVE MEANS CARRIED THEREBY BY REDUCING DIFFERENTIAL HEAT FLOW BETWEEN SAID ROTOR STRUCTURE AND SAID GASEOUS MEDIA. 